In most cases, these are hard-part film cassettes. The hard part consists regularly of an injection molding material such as PE, PP, PA, ABS, PMMA, PC or PVC. In the hard part, hose connections, connectors, chambers, passages and alignment devices are embodied by way of example. For using the blood treatment cassette, it is inserted into the blood treatment apparatus between a door and an actuator-sensor-unit of the blood treatment apparatus. By closing the door, it is brought into a so-called grouting or pressing position in which the film is pressed against the hard part and the blood treatment cassette together with the film are coupled in a spatially defined manner to the actuator-sensor mat of the actuator-sensor unit. When inserting the blood treatment cassette—also referred to as its equipping or as equipping of the apparatus—the main extension surface of the blood treatment cassette is adjusted and pressed or grouted against the main extension surface of the blood treatment apparatus (mostly the actuator-sensor mat). In the actuator-sensor mat and actuator-sensor plate (or unit), integrated actuators (components which are to be attached or connected to the actuator-sensor plate or mat, are also referred to herein as “actuator-sensor-sided”) may be able to exercise movements through the film, through which, for example, pump or valve functions may be realized. Properties of fluids which flow through the blood treatment cassette may be measured by at least one sensor optionally provided on the actuator-sensor-plate.